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Survival and mortality of bacteria in natural environments

par Servais, Pierre ;Vives-Rego, Jose;Billen, Gilles
Editeur scientifique Fry, J.C.;Day, M J
Référence Release of Genetically Engineered and Other Microorganisms, Cambridge University Press, Cambridge, Ed. 1, page (100-119)
Publication Publié, 1993-01-29

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Résumé :

IT HAS BEEN 15 YEARS since molecular biologists fust spliced DNA from one microbe ta another to create a recombinant bacterium. Developments in biotechnology have moved forward rapidly during these years, making it possible to construct genetically engineered micro-organisms (GEMs) that may provide useful applications. GEMs can be used in industrial processes, participating in the synthesis of products of economic or social important. Many laboratories are now working with recombinant microbes and many industrial plants will do so in the future. The risk of accidental release of such micro-organisms or of some part of their genetic material into the natural environment is therefore obvious and probably unavoidable. ln some cases, there might be reasons for concern about the survival or even growth of these GEMs in the environment. Conversely, some applications will involve the planned introduction of GEMs into natural habitats. Other chapters in this book provide numerous examples in agriculture and waste-water treatment. ln these cases, the survival of the released micro-organism is the first condition to be considered. Whatever the purpose might be, the fate of GEMs in natural environments, either feared or desired, is currently the subject of intensive questioning. To answer these questions, it is necessary to discuss a closely related and more general topic: the control of survival and mortality in the natural environment of micro-organisms in general. Two cases must be envisaged: (i) the case of natural, active, microbial populations, the dynamics of which depend on the equilibrium between growth and mortality rates; and (ii) the case of allochthonous bacteria, which may be unable to grow in the habitat where they have been introduced and may develop active or passive mechanisms for escaping normal mortality processes until better conditions are restored. Both cases are of interest from the point of view of the question set above and they will be discussed in parallel. The chapter will first attempt to define the concept of mortality in microbes, summarizing the rather scarce literature dealing directly or indirectly with this important question located at the intersect of philosophy and methodology. We will then discuss the various processes leading to mortality of microbes in natural environments, including predation, autolysis, physical or chemical injury, etc.; a summary of the data available to quantify the rate of bacterial mortality in the natural environment will be presented. The various strategies developed by microbes to overcome these mortality processes will then be presented and we will conclude with a brief discussion of the relevance of this information to the question set by the accidental or intentional introduction of GEMs in natural ecosystems. Partly because the literature is more rich in this field, and partly because of our own research interests, the emphasis of this chapter is on aquatic environments. Some data are presented to show that basically similar conclusions can be reached for the soil environment. We can feel less guilty about this aquatic bias because Chapter 11 specifically deals with the survival and dissemination of GEMs in soils.